Proteoglycans, isolated by dissociative guanidinium chloride (GuHCl) extraction of bovine lung, aorta, trachea, and tracheal mucosa, were compared. The high molecular weight fractions from Bio-Gel A15 chromatography contained mainly hyaluronic acid and chondroitin sulfate proteoglycan. Heparin and heparan sulfate were found only in the low molecular weight fractions. The lung high molecular weight chondroitin sulfate could only partly be separated from hyaluronic acid by DEAE-cellulose or DEAE-sepharose chromatography in sodium chloride gradients. Bio-Gel A15 column elution with 4M guanidinium chloride led to partial molecular weight lowering of the otherwise excluded peak. These results suggest that lung chondroitin sulfate proteoglycan may form aggregates with hyaluronic acid in a similar fashion to the hyaluronic acid aggregates shown to form with cartilage proteoglycan. Proteoglycans labeled with 35S-sulfate or 3H-glucoamine were isolated from rat lung cells grown from primary explants. Both the cell fraction as well as culture medium contained proteoglycans which migrated in the void volume of a Bio-Gel A15 column. These proteoglycans were not aggregates since chromatography in 3M GuHCl failed to cause molecular weight reduction. The proteoglycans were extensively degraded by trypsin and pronase treatment. The proteoglycan mixtures from the culture medium consisted mainly of 50% hyaluronic acid, 29% chondroitin-4/6 sulfate and 32% heparan sulfate. Further characterization of these fractions and comparison to proteoglycans of lung tissue are currently being performed.